In vivo observation of a photoprotection mechanism in plants

(Nanowerk News) If plants need light to perform the photosynthesis essential to their survival, how do they protect themselves against too much light? A joint CEA-CNRS research team at the Saclay Institute of Biology and Technology (iBiTec-S) is currently exploring this question, in collaboration with several other teams at universities in the United Kingdom and the Netherlands. Their research, which has potential applications in new solar energy and optoelectronics, is the subject of an article in the journal Nature ("Identification of a mechanism of photoprotective energy dissipation in higher plants").

Photosynthesis takes place in the chloroplast, a component element of the cell. The chloroplast membrane contains proteins which collect light energy and enable its transfer to photosystems where it is transformed into chemical energy. Under stress conditions (cold temperatures, dry weather), too much light energy is captured. This may generate a significant quantity of free radicals, which are toxic for the plant. Interestingly, there are mechanisms to protect the plant against this stress.

The iBiTec-S team has shown that under these conditions of strong light intensity, the plant's light-collecting proteins can transform into "photoprotectors" – i.e. proteins which dissipate excess light energy. Two different states are observed for this protein: one in which the protein captures energy and stores it and another in which it transforms energy into the heat. This property was demonstrated in vitro using proteins extracted from plants, as described in an initial article in Nature in 2005. The results of the current article go one step further. This time the phenomenon was observed in vivo, directly on the leaves of Arabidopsis thaliana after exposure to various light intensities. The new data, combined with ultra-rapid spectroscopy, also allowed the researchers to determine the chemical nature of the photoprotective molecules, which turn out to be luteins, a type of carotenoid pigment.

The discovery of these molecular mechanisms may lead to research applications in agronomy, but they may also play a role in optoelectronics research and in developing new solar technologies. These proteins essentially appear to be "nanoswitches", capable of transferring energy, or not transferring it, depending on exterior conditions.